The basic process for treatment of color photosensitive material is, in general, a color development process and a desilvering process. In the color development process, an exposed silver halide is reduced by a color developing agent to form silver and, at the same time, the oxidized color developing agent reacts with a color former (coupler) to produce a dye image. Silver formed in the process is oxidized by a bleaching agent in a subsequent desilvering process and further is subjected to actions of a fixing agent to be changed into a soluble silver complex which is then dissolved and removed. Thus, only a dye image is formed on the color photosensitive material.
The actual treatment of color photosensitive material includes, in addition to the above-mentioned basic treatment, various auxiliary processes to keep the photographic quality and physical quality of the image or to improve the preservability of the image. The auxiliary processes are, for example, a hardening bath, a stop bath, an image stabilizing bath, a washing bath, and the like.
In recent years, there, has been a strong demand in the industry for speeding up of treatment, that is, a reduction in the time required for treatment. In particular, a reduction in the time required for the desilvering process, which accounts for about half of the treatment time, has become a great problem.
As a bleaching agent, in general, potassium ferricyanide, dichromates, ferric chloride, ferric complex salts of aminopolycarboxylic acids, persulfates, and the like are known.
However, potassium ferricyanide and dichromates have environmental pollution problems relating to cyan compounds or hexavalent chromium, so that their use requires special treating equipment.
Ferric chloride has problems such as formation of iron hydroxide or stain formation in a subsequent washing process, so that there are many obstructions to their practical use.
The persulfates have problems such as a very weak bleaching action and a very long time required for bleaching, and further, laws such as The Fire Service Act impose limitations on the persulfate itself as a hazardous material, so that its storage requires various measures. Thus, persulfates are problematic and hard to use practically.
The ferric complex salt of aminopolycarboxylic acid, in particular, a ferric complex salt of ethylenediaminetetraacetic acid, is the bleaching agent now in widest use, because it has no environmental pollution problems and no restrictions are imposed on its storage. However, the bleaching power of the ferric complex salt of aminopolycarboxylic acid is not always sufficient.
Hitherto, as a means to speed up the desilvering process, there has been known a bleach-fixing bath mentioned in German Patent No. 866,605 which comprises one solution containing a ferric complex salt of aminopolycarboxylic acid and a thiosulfate. In the bleach-fixing bath, however, the presence of both a ferric complex salt of aminopolycarboxylic acid having weak oxidizing power (bleaching power) and a thiosulfate having reducing power in the same bath results in markedly weakened bleaching power. Thus, it is very difficult for the bleach-fixing bath to sufficiently desilver a color photosensitive material having high sensitivity and a high silver content, so that the bleach-fixing bath has major disadvantages and cannot be used in practice.
On the other hand, to increase bleaching power, the addition of various bleach accelerating agents to a bleaching bath, a bleach-fixing bath, or a bath preceding to those has been proposed.
As such bleach accelerating agents, there may be mentioned, for example, mercapto compounds as mentioned in U.S. Pat. No. 3,893,858, British Patent 1,138,842, and Japanese Patent Application (OPI) No. 141623/78 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application"); compounds having a disulfide bond as mentioned in Japanese Patent Application (OPI) No. 95630/78; thiazoline derivatives as mentioned in Japanese Patent Publication No. 9854/78; isothiourea derivatives as mentioned in Japanese Patent Application (OPI) No. 94927/78; thiourea derivatives as mentioned in Japanese Patent Publication Nos. 8506/70 and 26586/74; thioamide compounds as mentioned in Japanese Patent Application (OPI) No. 42349/74; dithiocarbamic acid salts as mentioned in Japanese Patent Application (OPI) No. 26506/80; and arylenediamine compounds as mentioned in U.S. Pat. No. 4,552,834.
Of these bleach accelerating agents, there are certainly some which accelerate bleach, but the effective ones are not satisfactory from a practical viewpoint, because they are expensive or have insufficient stability in a bath having bleaching power.
Combining two or more compounds of ferric complex salts of various aminopolycarboxylic acids has been mentioned in Research Disclosure, RD No. 24023 (April, 1984) and Japanese Patent Application (OPI) No. 230653/85, but they also cannot display a sufficient bleach accelerating effect.